Standard 5N red gold according to ISO standard 8654 (composition: Au750Cu205Ag45) is currently the most used alloy in the timepiece market, particularly for making external timepiece parts, typically watch cases, bracelets, etc. Unfortunately, this red gold alloy, which has an interesting attractive appearance, discolours over time and slowly changes from its initial red colour to yellow. This phenomenon frequently leads to claims from clients who are dissatisfied with this transformation. The cause of the discolouration is the selective dissolution of Cu close to the surface causing an increase in the concentration of Au at the surface which turns the alloy yellow. There is already known from EP Patent Application No. 1512766A1, a red gold alloy with added platinum, which increases resistance to discolouration compared to prior red gold alloys. However, although more slowly, this gold alloy also exhibits a colour change which can be improved in certain wear conditions, such as when it is subjected to perspiration or acid rain. Further, it is known that platinum is an element with a very high melting point (1768° C.) requiring preparations of mixtures with other specific elements (Au and/or Cu) to lower its melting temperature, which makes the implementation of the alloy more complicated and more expensive. Indeed, without the addition of these alloy elements, platinum does not dissolve homogeneously in gold and makes it mechanically more difficult to deform for certain horological applications.
Thus, platinum remains a very expensive material which increases the cost of the alloy.